1. Field of the Invention
This invention relates generally to composite lid closure arrangements for use with containers. More specifically, the lid of the present invention includes a semi-rigid plastic ring and a central panel coated on two sides with a plastic material which is bonded, preferably ultrasonically, to the ring.
2. Description of the Prior Art
U.S. Pat. No. 3,397,814 discloses a basic composite lid having a central panel and plastic lid ring to engage a container rim. Unlike the invention described herein, the central panel of the '814 patent, made preferably of fibrous paper board, has no plastic coating on either side. The '814 patent uses injection molding, not ultrasonic bonding, to bond the central panel to the plastic lid ring.
In U.S. Pat. No. 4,141,463, a plastic lid is ultrasonically bonded to a container rim for hermetically sealing the container. The container rim was previously coated with a sealable material to accomplish ultrasonic bonding. However, the '463 patent does not deal with the concept of creating a composite lid by ultrasonically bonding a central panel to a plastic ring to form the lid.
Other inventions for achieving a closure arrangement using a composite lid or a membrane to hermetically seal a container include U.S. Pat. Nos. 4,418,834; 4,442,971 and 4,448,345. In each of these patents, the composite lid is built using an injection molding process for bonding the central panel to the plastic lid ring.
The '834 patent, for example, describes a laminated membrane structure comprising a foil disk coated on top and bottom with sealable material. A central panel is bonded to a plastic lid ring through injection molding. The laminated membrane structure is bonded to the central panel and container rim by inductively heating the foil. No ultrasonic bonding is used to bond the central panel to the plastic lid ring or to bond the laminated membrane structure to the central panel or container rim.
The '345 patent discloses a composite lid comprising a central panel which is bonded to a plastic lid ring by insert injection molding. A membrane, comprising a top layer of saran and a bottom layer of polyethylene, is attached to the bottom of the central panel with a conductive wax at the peripheral edge of the panel and membrane. The conductive wax is used for radio frequency bonding of the membrane to the central panel and container rim. Once again, injection molding, not ultrasonics, is used to bond the central panel to the plastic lid ring and radio frequency is used to bond the membrane. Nothing is ultrasonically bonded.
The '971 patent discloses another sealable enclosure that utilizes a plastic lid ring bonded with a central panel through injection molding. Heat sealing is also used for bonding, but not ultrasonics. The '971 patent goes on to describe how a hermetic seal is retained when internal gasses push the middle of the container lid up. The invention described herein, however, does not utilize the same mechanism for this feature. Instead, in the invention described herein, a larger depending vertical skirt and a vertical appendage above the central panel add mechanical strength to the plastic ring. The additional strength of the plastic ring resists distortion due to upwardly or downwardly pushing gas pressure thus retaining contact with the container rim.
Finally, U.S. Pat. No. 4,289,252 discloses a closure arrangement for two plastic rims. One soft rim, on the lid, and one hard rim, on the container, are forced together to hermetically seal the container. No composite lid is described and the sealing mechanism does not use heat or ultrasonios. The stacking of plastic lids described in the '252 patent does not involve the stacking of containers as described in the present invention.
From the above analysis, it can be seen that the prior art patents, individually and as a whole, do not disclose a composite lid enclosure arrangement comprising a central panel with coating on two sides which is ultrasonically bonded to a plastic ring.